1. Field of the Invention
The present invention relates to an active matrix substrate in which a picture element electrode and an electrode respectively located above and below an interlayer insulator are connected to each other through a contact hole of the interlayer insulator and another electrode is formed opposite the electrode for forming an auxiliary capacitor, and particularly relates to a countermeasure for causing less leakage between the electrodes even if a defect is formed in a control insulator between the electrodes in forming the contact hole.
2. Description of the Related Art
In recent years, liquid crystal display devices are small in size, thickness, power consumption, and weight as their features and, therefore, are employed in a variety of electronic appliances. Particularly, an active matrix liquid crystal display device using a switching element as an active element exhibits display characteristics equivalent to a CRT and, accordingly, is widely employed in OA appliances, such as a personal computer, AV appliances, such as a television set or an on-vehicle monitor for a car navigation system, mobile phones, and so on.
FIG. 8 and FIG. 9 show an example of a structure of an active matrix liquid crystal display device using a TFT (Thin Film Transistor) as a switching element, which is known from Patent Document 1, for example. FIG. 8 is a plan view of a structure of one of picture element regions of an active matrix substrate when viewed from a counter substrate arranged opposite the substrate, and FIG. 9 shows an entire structure of the liquid crystal display device in which a liquid crystal layer is arranged between the substrates and is a sectional view corresponding to an enlarged sectional view taken along VIII-VIII in FIG. 8.
This liquid crystal display device includes an active matrix substrate 100 including a TFT 160 in each picture element region; a counter substrate 300 arranged so as to be opposed to the active matrix substrate 100; and a liquid crystal layer 400 arranged between the substrates 100 and 300. In the active matrix substrate 100, a gate electrode 160a and a source electrode 160c of the TFT 160 are connected electrically to a gate signal line 120 and a data signal line 150, respectively. A drain electrode 160d of the TFT 160 is connected electrically to a picture element electrode 180 located on an interlayer insulator 170 through a contact hole 70a formed in the interlayer insulator 170, the interlayer insulator 170 being provided so as to cover the gate signal line 120, the data signal line 150, and the TFT 160.
Further, under the contact hole 170a (the lower part in FIG. 9), an auxiliary capacitor counter electrode 130 (hereinafter referred to as a Cs counter electrode) is arranged so as to be opposed to a part of the drain electrode 160d with an gate insulator 140 interposed so that the drain electrode 160d and the Cs counter electrode 130 form an auxiliary capacitor.
Referring to the active matrix substrate 100, in the case where a defect, such as a pinhole, is formed in the drain electrode 160d, another defect may be formed in the gate insulator 140 through the defect in the drain electrode 160d in forming the contact hole 170a in the interlayer insulator 170 by etching or the like. As a result, leakage occurs between the drain electrode 160d and the Cs counter electrode 130 through the defect in the gate insulator 140.
For taking this into consideration, conventionally, the contact hole 170a is arranged in a region other than the region of the Cs counter electrode 130 while the drain electrode 160d is extended to the contact hole 170a so as to be connected to the picture element electrode 180, as disclosed in Patent Document 2 and as shown in FIG. 10 as a plan view. In this way, the Cs counter electrode 130 is not formed in the region of the contact hole 170a so that occurrence of leakage between the drain electrode 160d and the Cs counter electrode 130 is suppressed even if a defect is formed in the gate insulator 140.    Patent Document 1: Japanese Patent Application Laid Open Publication No. 09-230380A (Pages 5 and 6 and FIG. 2)    Patent Document 2: Japanese Patent Application Laid Open Publication No. 2002-55360A (Page 6 and FIG. 4)